Cyrstal growing is a significant precursory activity in the manufacture of semiconductor devices. Semiconductor crystal growing processes have been improved to yield single-crystal semiconductor ingots which may range, for example, in excess of 125 mm in diameter and between one and two meters in length. Various commercially available models of crystal growing furnaces supportive of the commonly followed crystal growing processes are functionally and structurally similar. A typical crystal growing furnace features a crystal growing chamber in the base of the furnace. The crystal growing chamber typically houses a crucible, heating elements to melt down and maintain as a melt a charge of a crystalline material fed into the crucible, and mechanisms for rotating the crucible to control the uniformity of the heat flux in the melt during the crystal growing process.
Rising above the crystal growing chamber is a towering structure of a crystal pulling chamber. The crystal pulling chamber typically is an upright, substantially cylindrical enclosure terminating in an upper structure of a crystal pulling mechanism. The crystal growing chamber and the crystal pulling chamber are in communication with each other during the growing process. As a crystal ingot continues to grow from the melt in the growing chamber, the crystal pulling mechanism raises the ingot at at a rather constant rate into the crystal pulling chamber. Typically, an operator removes the grown crystal ingot from such described furnace through a side access door in the crystal pulling chamber. A port between the crystal growing chamber and the crystal pulling chamber may be closed while the normally hermetically sealed side access door of the pulling chamber remains open.
Removing crystal ingots from growing furnaces has in the past presented problems. Typically, the operator in removing a grown ingot, actually carries the ingot through the access door after disconnecting the neck of the ingot at the seed end from the crystal pulling mechanism. As technology progresses toward ever larger ingots, the weight of the grown ingot, as well as its residual elevated temperature at the time of its removal, make such manual removal a less than desirable operation.
U.S. Pat. No. 4,350,560 to Helgeland et al. discloses apparatus for and a method of handling crystals to remove them from growing furnaces by transferring a crystal ingot vertically downward to a transport mechanism. The disclosed apparatus and its related method avoid the problems typically associated with removing crystal ingots through the described side access doors. Unfortunately, the crystal handling method described in U.S. Pat. No. 4,350,560 also presupposes a furnace structure which has an accessibility below the crystal pulling chamber to accommodate the height of the transport mechanism as tall as the ingot is long. The crystal pulling mechanism and the crystal pulling chamber of the furnace as disclosed by the patent are simply movably mounted to become laterally offset from vertical alignment with the crystal growing chamber and into alignment with the transport mechanism. However, the solution provided by the above-mentioned patent does not apply to a large number of growing furnaces which are installed with insufficient space below such laterally moved crystal pulling chambers, or which have otherwise limited access to remove crystal ingots vertically from the crystal pulling chambers.
Furnace structures with such limited access are found particularly in installations of comparatively large structures of the latest commercially available high production furnaces. The crystal pulling chambers of such large furnaces typically extend through substantially the entire height of a factory level. In many instances, permanent, mezzanine-type, service platforms are built adjacent to upper portions of such furnaces to provide convenient access for servicing the pulling mechanisms of the furnaces. A vertical removal of crystal ingots from such large and often inaccessible furnace structures presents formidable problems. Consequently, the removal of ingots from most furnaces has up to now remained a manual task.
Problems encountered in attempting to remove crystal ingots by mechanical means from furnaces which have side access doors are related in part to the smoothness of the surface of the grown crystal ingots and to the brittleness of the crystalline material. Stresses are imparted to the crystal when the ingots are gripped too firmly to generate a sufficient friction force. An excessive contact force against the ingot coupled with a bending force tend to result in crystal fractures. If the ingots are gripped less firmly, they may slip and fall. Problems in gripping crystal ingots with mechanical grippers are further complicated by variations in length to which different crystal ingots are grown in successive operations of a growing furnace. Often the growing process is terminated before a crystal ingot has reached its maximum possible length. Consequently, crystal ingots of various lengths and weights need to be removed from the crystal growing furnaces.